One of the letters sent to Emerson's deputy chairman, Alan White, was opened by his wife. It read: "You profit from animal torture, you are a sick, evil, perverted deviant. The day of reckoning has now arrived for you."

There were other victims who worked for Emerson, which rented office space to a Japanese pharmaceutical company called Yamanouchi.

The court heard all Lawrence's letters were similar, another read "You are a sick, evil, perverted deviant. You are now a legitimate and priority ALF target. The animal rights militia exists just for filthy, animal-abusing scum like you. You have been warned."

Prosecutor Greg Perrins said: "The case concerns the sending of anonymous, threatening and aggressive letters to members of the public thought by this defendant to have a connection, however vague or tenuous to Huntington Life Sciences, which is a laboratory facility in Cambridge.

"It carries out research work for the pharmaceutical industry, some of which involves testing on animals.

"The purpose of the letters appeared to be to intimidate the recipients such that they would give up their jobs.

"In many cases the connection was extremely vague and tenuous - there were courier firms threatened, cargo companies and companies that leased out office space for companies who themselves had a connection with Huntington Life Sciences - so two steps away."

Lewes Crown Court, in Sussex, heard how one of her victims was so terrified he employed a private security firm to protect his family after Lawrence wrote: "Your life will be made a living hell until you stop abusing animals for profit, you evil, perverted scum."

Many of Lawrence's victims had already suffered at the hands of animal rights activists, who had been conducting a campaign of fear against anybody linked to animal laboratories.

The mother-of-one, an Animal Liberation Front supporter, admitted causing a public nuisance and was jailed for eight months after judge described her as an "intelligent woman" who was "wholly respectable" in other parts of her life.

Mr Perrins said she had links to an organisation called SHAC - Stop Huntington Animal Cruelty - and was once stopped by police wearing an Animal Liberation Front badge.

He added that the recipients of the letters had in the past been subject to other forms of harassment including bomb hoaxes and letters being sent to neighbours accusing them of being paedophiles.

Some victims resorted to having their mail re-directed, having it x-rayed and having CCTV cameras installed at their home address.

The court heard that Lawrence was traced after a recipient of a threatening letter recalled seeing a similar post-mark on a non-threatening letter sent by her on an earlier date.

She had no previous convictions, but was cautioned in 2000 for pursuing a course of conduct by posting a malicious leaflet through the letterbox of a Huntington Life Sciences shareholder.

Defending, Dora Belford said Lawrence has a son at university, her father was a senior officer in the Army and her husband had also been a "high-up" officer.

She added Lawrence, of Sunbury, Middlesex, had become involved in animal rights campaigns after seeing a TV programme in 1999.

"My client accepts the content of them was intimidating but in fact there was no action taken by anyone which was directly referable to these letters," she said.

Ms Belford added that Lawrence was not part of the "hierarchy" in animal rights groups such as SHAC.

"She was nicknamed Lady Penelope and Fluffy. That is how she was viewed by the people in these campaigns. She was very much on the periphery."

Sentencing her to eight months, Judge Richard Hayward said: "These were designed to frighten and intimidate and were part of a wider campaign waged by SHAC.

"I accept you may not have been high in the hierarchy of SHAC but you were part of a co-ordinated campaign of intimidation.

"You are undoubtedly an intelligent woman with good qualifications and wholly respectable in other parts of your life.

"I think you lack insight into the effect these letters would have on people.

"The campaigns which you have supported have generated considerable emotion and generated violence and people must understand that believing in a cause does not justify unlawful activities."

Judge Hayward also imposed a five year Anti-Social Behaviour Order banning her from going within one mile of Huntington Life Sciences, from contacting anyone involved in the company or its agents.

She was also banned from contacting anyone involved in the proposed building of an animal-testing laboratory at Oxford University.